In a known tractor of this constructional type (DE-OS 35 21 429 [=German Offenlegungsschrift=Patent Application Files laid open to public inspection]) the holding down members are horizontal bow-shaped members which are arranged so that prior to the nose wheel receiving procedure they are adjusted to a height corresponding to the diameter of the nose wheel so that in this position they constitute positive firm stops for the nose wheel, which overlap the nose wheel from above. Yet in this case it was ascertained that a reliable clamping of the nose wheel by such rigid holding down members is not possible. This is so because during starting and pulling by the tractor it will result that due to the elasticity of the arrangement for one thing and above all because of the air-filled pneumatic tire of the nose wheel for another thing there is some self-movements may occur which may be so considerable that the nose wheel will possibly work out itself from its clamped condition.
Furthermore, from DE-OS 35 34 045 is known a tractor having arc-shaped holding down members which are mounted to be movable by journal means on levers above the shovel so that they will be laid from above onto the nose wheel so that they can follow the nose wheel during its movement on the shovel. Yet this known arrangement is mounted above the nose wheel which is being held so that this arrangement will be so high that collisions with aircraft members and in particular with the nose wheel suspension are to be feared. Apart from this, the blocking of the holding down members takes place hydraulically so that they will merely constitute a rigid stop.
The problem underlying this invention is seen in providing a tractor of the constructional type mentioned in the first paragraph hereinabove, which has a holding down member by means of which a perfect fixing of the nose wheel onto the shovel can be achieved without endangering the aircraft members arranged above the nose wheel.